1. Field of the Invention
The present invention relates to a transflective liquid crystal display panel and more particularly in a transflective liquid crystal display panel which can render consistence of the transmittances on both transmission region and reflective region thereof under the same driving voltage.
2. Description of the Prior Art
As known, conventional thin film transistor (TFT) liquid crystal display (LCD) panel scheme includes opposite upper and lower substrates and a liquid crystal (LC) layer which is constructed by sealing a number of liquid crystals molecules between the upper and lower substrates. The upper substrate is equipped with color filter and common electrode thereon. With a pixel electrode and a thin film transistor for each corresponding pixel, the lower substrate is equipped as a TFT array substrate. By applying a driving voltage on the thin film transistors of the lower substrate, an electric field is induced between the common and pixel electrodes to control direction or tilt change of the liquid crystal molecules so as to affect light transiting direction. For example, when relative low and high voltages are respectively applied on the common and pixel electrodes of the upper and lower substrates, the electric field lines induced from the pixel electrode would distribute over the LC layer. The distributing directions of the electric field lines could vary tilt angles of the liquid crystal molecules allocated within the LC layer. In cases the direction-varied LC molecules would be always kept parallel or perpendicular to the electric field lines, depending upon whether a dielectric constant anisotropy (Δ∈) of the LC molecule is positive or negative. To broaden visual-angle boundary of the panel, various kinds of commonly-used liquid crystal includes, for example, Twisted Nematic (TN) type, a Vertical Alignment (VA) type and an In-Plane-Switching (IPS) type. Most of the VA type LC is a negative LC molecule with an elongated ellipsoidal shape. A longwise axis and a short axis of the ellipsoid-shaped LC are respectively applied to get different refractive characteristics for displaying different grays. For example, when none of the driving voltage is applied, the VA type LC is kept perpendicular to the upper and lower substrates to bar pass of light through the LC. This causes that the frame of the display panel appears black image. On the contrary, when the driving voltage is applied, different electric field directions are induced in light of whether the common and pixel electrodes are allocated on the same substrate or not. Because the induced electric field lines should be perpendicular to the longwise axis of the LC molecules, the different tilt and directions of the LC molecules would be determined (i.e. the longwise axis becomes parallel to the substrate) and thereby permit pass of light through the LC.
Beside a Multi-Domain Vertical Alignment (MVA) type LC is disclosed presently, which makes a technological improvement on the basis of the VA type LC so as to broaden visual-angle boundary of the panel. The improvement is to additionally form one or more than one protrusion (or called ‘bump’) on the electrode of the upper and/or lower substrate of the panel. When none of the driving voltage is applied, the longwise axis of the LC distributed within the LC layer is kept perpendicular to the upper and lower substrates. Each pixel is constituted by numbers of corresponding vertical LC molecules, except that the other LC molecules adjacent around the protrusion suffer local effect to tilt toward a specific direction or angle, rather than a vertical direction. As long as the driving voltage is applied, several inclines formed with the protrusion can influence the adjacent LC molecules to tilt toward different directions (such as opposite or complementary directions), as dividing each pixel into different displaying domains, such that the different-directional LC molecules distributed in the different domains can be complemented with each other to broader visual angle bound.
It notes that after the ray pass through LC molecules between the upper and lower substrates, it commonly invokes appearance of two kinds of refractive lights, one of which is Ordinary Ray defined that a light wave having a light axis perpendicular to an electric field component has an ordinary refractive index (no); the other is Extraordinary Ray defined that a light wave having a light axis perpendicular to an electric field component has an extraordinary refractive index (ne). A common LC molecule has both of the refractive indexes (no), (ne). A difference between both of the ordinary and extraordinary refractive indexes (no), (ne) is defined as a refraction change value (Δn) of birefringence. Due to occurrence of a speed difference between the ordinary and extraordinary rays during passing through LC molecule, a phase retardation phenomenon appears between the ordinary and extraordinary rays, wherein a phase retardation of the whole LC layer can be represented by a total retardation change value which is defined as a product of the refraction change value multiplying a cell gap value (Δn×d).
Nevertheless, distributing direction of the electric field lines can be varied by a LC-controlling technology so as to change position of a longwise axis of the corresponding LC molecule. While the ray passes through such a LC molecule, a different refraction change value can be therefore achieved. For example, when a conventional VA type LCD panel is in the on state, the electric field lines induces the longwise axis of the LC molecules to tilt in 90 degree from a perpendicular to a parallel with relation to the substrate, and thereby the ray could progress along the short axis of the LC molecules to minish the phase retardation resulted from both of the ordinary and extraordinary refractive indexes.
Based on different light sources and light-controlling processes, commonly-known liquid crystal display panel can be distinguished into a transmission type, a reflective type and a transflective type. Since the transmission type LCD panel has to use a backlight module for light source supply, this causes more power consumed. Besides the transmission type LCD panel possibly becomes dark under illumination of brightened light from the outdoor, and therefore can not provide bright and clear image display. Differently from use of backlight source, the reflective type LCD panel is additionally disposed a reflector thereon and therefore utilizes an external light from the environment to achieve the illumination for implementation of image display. Although the reflective type LCD panel has more power savings, its definition is easily affected by brightness of the external light. To eliminate the problem of either of the transmission type or reflective type, the transflective type LCD panel is proposed as shown in FIG. 1A, which includes a first substrate 10, a second substrate 12 with thin film transistors 121, and a LC layer 14 having a single cell gap (d) formed between both of the first and second substrates 10, 12. Each pixel constituted between both of the first and second substrates 10, 12 can be divided into a transmission region 100 and a reflective region 120 for concurrently obtaining the features of both the transmission type and reflective type LCD panels. The transmission region 100 employs a built-in backlight as a light source needed for image display, and therefore is suitable to use for the indoor environment. The reflective region 120 employs a reflector to reflect the ray from the outdoor environment as a light source, and therefore is suitable to use for the outdoor environment. Accordingly, the transflective type LCD panel can retain the same definition and brightness display, regardless of the indoor or outdoor, and provide a power-saving function.
However, when the conventional transflective type LCD panel is in a reflective mode such as the outdoor, an external ray (R) enters the LC layer 14 having a cell gap (d) in the reflective region 120, and then is reflected back by the reflector to the human eyes. Since the ray (R) passes through the cell gap (d) twice as approximate two-time cell gaps (2d), a refraction change value (ΔnR) of the reflective region 120 can be therefore achieved. Oppositely, when the conventional transflective type LCD panel is in a transmission mode such as the indoor, a ray (T) emitted from a backlight source located on the transmission region 100 passes through the same cell gap (d) once to enter the human eyes, a refraction change value (ΔnT) of the transmission region 100 can be therefore achieved. The refraction change value (ΔnT) of the transmission region 100 is approximately identical with refraction change value (ΔnR) of the reflective region 120 (i.e. ΔnT≈ΔnR) because both of the regions 100, 120 use the same liquid crystal and LC tilt. However, this causes a difference between the phase retardation of the transmission region 100 and the phase retardation of the reflective region 120 (i.e. ΔnT×d≠ΔnR×2d). If the LC tilt of both the regions 100, 120 are different, it would cause the difference between the refraction change values of both the regions 100, 120 (i.e. ΔnT≠ΔnR) and the difference between the phase retardations of both the regions 100, 120.
When the phase retardations of both the regions 100, 120 are different from each other, it is known from a transmittance-to-voltage coordinate diagram as depicted in FIG. 1B that a reflective-mode curve 20 and a transmission-mode curve 22 have different tracks and distributions from each other. It means that there are two different transmission ratios Tr, Tlow respectively appearing in both the regions 100, 120 of the panel under the same driving voltage. On the other respect, a driving voltage (Vt) used to generate a brightness (Tt) required for one of the modes is different from another driving voltage (Vr) used to generate a brightness (Tr) required for the other mode. Even any one of the modes obtains required brightness, yet the other mode has to sacrifice its optical display such that there might be problems of insufficient brightness or yellowing in gray display.
As shown in FIGS. 2A and 2B, conventional transflective type LCD panels 2A and 2B utilize controllable fabricating process to form dual cell gaps (d1, d2) on where is related to the transmission region and the reflective region on a substrate 26 having a driving transistors or a substrate having a color filter. For example, multi cell gaps are formed on thin film transistor array (MOA) or multi cell gaps are formed on the color filter (MOC), whereby the retardation change values of both of the transmission and reflective modes can be balanced to render gradual consistence between the ratios of the driving voltages to the transmittances in both of the transmission and reflective modes (i.e. ΔnT×d≈ΔnR×d/2). However, to make different cell gaps from each other, the complexity of structural-fabricating process easily causes lower yield and higher expense, and also causes a light leakage on a bound between the transmission and reflective regions to get poor display definition. Besides other conventional transflective type LCD panel applies different driving voltages to render LC tilt difference between the transmission and reflective regions but is resulted in more complex design thereof.